1. Field of the Invention
This invention relates to apparatus and methods for the detecting of and identifying of overheated materials such as electrical insulation used in a gas-cooled dynamoelectric machine.
2. Description of the Prior Art
In recent years, a device commonly known as a generator condition monitor or gas stream monitor (Ref: U.S. Pat. No. 3,427,880 issued Feb. 18, 1969 and U.S. Pat. No. 3,573,460 issued Apr. 6, 1971) has been used to detect overheating within a dynamoelectric machine and overheated electrical insulation through the presence of thermoparticulates in the dynamoelectric machine's cooling gas. Thermoparticulates are formed in dynamoelectric machines as a product of thermal degradation of insulation. In the monitor, the molecules of a steadily flowing sample of the cooling gas are ionized to a state of equilibrium with a source of alpha-particles in an ionization chamber. The ions are then completely electrodeposited when the gas is passed between two charged electrodes in a collection chamber. The electrodeposition current is then amplified and applied to a recorder where it is continuously monitored. If there have been thermoparticulates entrained within a given sample, some of the ions will attach themselves to the thermoparticulates causing the number of free ions to decrease. The charged thermoparticulates have a much lower mobility as compared to the cooling gas ions, very few will be electrodeposited resulting in a decrease in the total electrodeposition current. This decrease is used as an indication of the presence of thermoparticulates caused by overheating.
When the generator condition monitor or gas stream monitor detects particulate matter in the gas stream caused by overheating of insulation, a signal is observed on the monitor's chart. A sample of the cooling gas is usually passed through a three-part collection arrangement to trap out particulate matter. (Ref. U.S. Pat. No. 3,972,225 issued Aug. 3, 1976). After the collection of the sample, the collection assembly may be sent to an analysis laboratory for identification. The location of the fault within the generator is then identified by employing mass spectroscopy. The generator particulate mass spectrogram is compared to standard spectrograms which are fingerprints of the different types of insulation used in the generator. Thus, the insulation that has undergone thermoparticulation can be identified.
There are four major disadvantages in the use of laborator mass spectroscopy for fault location within a generator; these are:
1. The generator condition monitor is far more sensitive than a mass spectrometer; it has been estimated that a factor of 10.sup.5 exists in favor of the gas steam condition monitor sensitivity.
2. A severe loss in particulate signal strength has been observed due to evaporation losses during transportation of the collection assembly from the location of the dynamoelectric machine to the laboratory that will perform the analysis.
3. The turn-around time for such an analysis can take up to several days; this means that the start-up of the machine is delayed by at least this amount of time.
4. This method of service and analysis is expensive.